Soot blower operation for vapor generator furnaces



E. P- PETIT Sept. 27, 1966 SOOT BLOWER OPERATION FOR VAPOR GENERATORFURNACES Filed Sept. 28, 1964 2 Sheets-Sheet l l I l I I I I i i I I III. |.l|ll|||||| J G Z n 0 u 2 MM 7 3 ww f 7 Z 2 W p W x ww 5 5 W M m zc w T); Qlmz 4 was www 1 Z 3 PWM 5w r NH 5 3 ,3 F51 MIIH W I; llill L MMM 7 I I l I I I I l I I l I I I I I I l l l I] 0 .M 7m 62 0 W 7 W? y j 5Z vmmfim if 1 VWL 1H 3 T I 3 H U d i w z 1F 1F 7 r||1l| 9 F ll I II u ll a l r I i l 1 I i I l r E. P. PETIT FLOW SOOT BLOWER OPERATION FORVAPOR GENERATOR FURNACES Filed Sept. 28, 1964 FIG-2 Sept. 27, 1966 r: m:J Q18 m h M w? Z 9 n 5004 LL L United States Patent 3,274,979 SOOTBLOWER OPERATION FOR VAPOR GENERATOR FURNAClEfi Elwood P. Pctit,Windsor, Conn, assignor to Combustion Engineering, luc., Windsor, Conn,a corporation of Delaware Filed Sept. 28, 1964 Ser. No. 399,559 11Claims. c1. 122-392) This invention relates to vapor generator furnacesand particularly to a method and apparatus for furnace wall soot bloweroperation.

In steam generating units burning coal or other ash bearing fuels therehas always been a problem with ash deposits on the walls of furnaces.These deposits effectively insulate the walls, decreasing the furnaceheat absorption, disturbing the balance of heat absorption throughoutthe unit, and in some cases, decreasing the efliciency of the unit.Furthermore, excessive buildup of this ash can lead to conditions wherethe slag bridges over the burners requiring a shutdown for cleaning and,in some cases, a heavy accumulation of slag suddenly falls off the wallsdamaging the floor of the furnace. This problem is becoming morecritical since units are being built with high furnace heat releaserates and poorer quality coals are being burned.

Generally the furnace wall soot blowers are set for sequential operationand their application is dictated by general furnace performanceconditions. A typical furnace wall soot blower is described in US.Patent 2,662,241 and typical methods of operating these blowers areshown in US. Patents 2,811,954 and 3,137,278.

As the furnace walls become dirty the gas temperature leaving thefurnace tends to increase and superheaters located in the gas streamproduce steam of an increased temperature. Various means are used tocontrol this steam temperature in order to compensate for the dirtinessof the furnace. This includes methods such as tilting burners, spraydesuperheating, gas recirculation and superheater gas bypasses. As thefurnace dirties up, the control means operates to maintain a preselectedsteam temperature. The position of the steam temperature controller issensed and when it reaches a predetermined position, it is known thatthe furnace walls have reached a particular over-all dirtinesscondition. At this time all of the furnace wall blowers are operated toclean the walls with the steam temperature controller moving to anearlier position to maintain steam temperature. As the furnace dirtiesup again, this cycle is repeated.

The deposition of ash on the furnace walls is not uniform with therebeing certain areas that tend to dirty rapidly and others which remainrelatively clean. General soot blowing of the entire wall accomplisheslittle in the relatively clean areas. The operation of the soot blowersin these clean areas uses expensive soot blowing media and prolongs thetime of the actual soot blowing cycle. Since there is always thepossibility of tube errosion due to the soot blower action, operation ofsoot blowers in a clean furnace zone creates an unnecessary risk with nocompensating advantage.

In a circuit lining the walls of a furnace the tubes must be joined insome manner to maintain the over-all structure. This may be done bywelding these tubes to bars which cross them transversely on the casingside, or as is now more often done by welding the adjacent tubescontinuously throughout their length. Uneven slagging conditions on thefurnace side of these tubes results in uneven heat absorption which isreflected in an unbalance of the temperature of the fluid temperaturespassing through the furnace wall. This temperature unbalance creates acondition where the hotter tubes want to expand with relation to thecolder tubes, setting up stresses in the overall furnace wall structurein various locations. Repeated slagging and cleaning of the furnacewalls will cause a cycling of these stresses and lead to fatiguefailures even at relatively low stresses.

Such a circuit may be controlled so that the outlet temperature ismaintained constant regardless of the variations in heat absorption.This is accomplished by measuring the outlet temperature and varying therelative flow in accordance with the heat absorption through theparallel groups of tubes to maintain the temperatures equal. In such asituation a group of tubes receiving high heat absorption will containthe same temperature fluid as the other tubes but it will be operatingat a higher heat absorption rate. This higher heat absorption rate,therefore, causes a higher metal temperature in these circuits creatingthe same type expansion problem as previously discussed although oflesser magnitude.

In my invention a furnace wall circuit is divided into a plurality ofgroups of tubes, with particular soot blowers being associated with eachgroup. The heat absorbed in each group is determined in some manner suchas temperature or fluid flow measurements thereby indicating which ofthese groups of tubes have excessive ash accumlations along theirlength. In response to this indication of heat absorption the propersoot blowers are operated corresponding to the particular low heatabsorption group so that those circuits with the heaviest ashaccumulation may be cleaned first.

It is an object of my invention to provide a method and apparatuswhereby soot blowers may be operated for maximum furnace wall cleaningefficiency by ope-rating those in the dirtiest zones first, therebyreducing the amount of soot blowing necessary.

It is a further object to provide a method and apparatus for operatingsoot blowers so as to obtain more uniform heat absorption andtemperatures throughout the furnace walls.

Other and further objects of the invention will become apparent to thoseskilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises anarrangement, construction and combination of the elements of theinventive organization in such a manner as to attain the resultsdesired, as hereinafter more particularly set forth in the followingdetailed description of an illustrative embodiment, said embodimentbeing down by the accompanying drawing wherein:

FIGURE 1 represents a once-through unit with the soot blower actionresponsive to the temperature leaving various groups of tubes within thefurnace; and

FIGURE 2 represents a once-through unit in which the soot blower actionis responsive to the flow through the various groups of tubes within thefurnace walls.

Fuel is delivered through tilting burners 2 into the furnace 3 wherecombustion takes place with the products of combustion passing outthrough flue 4 exhausting through a stack (not shown). The walls of thefurnace are lined with furnace wall tubes 5 which convey fluid from theinlet headers 7 to the furnace wall outlet headers 8. This fluid entersthe walls at a temperature of about 670 F. and a pressure of 4100 p.s.i.reaching the outlet headers at a temperature of about 800 F. and at apressure of 4000 psi.

This fluid which is now steam is conveyed through cross-over pipe 9 tothe superheater inlet header 10 and thence through the superheatingsurface 12 and through the outlet steam pipe 13. The combustion gasespassing through the flue 4 superheat the steam passing through heatingsurface 12 to a temperature of about 1050 F.

This steam is conveyed to a high pressure turbine (not shown) andreturned to the reheat inlet header 14 at a temperature of about 650 F.and a pressure of about 700 p.s.i. This steam passes through heatingsurface 15 located in flue 4 and is heated to a temperature of about1000 F. This steam is then conveyed through steam line 17 to the lowpressure turbine (not shown). These two turbine sections are connectedto drive an electric generator (not shown).

Furnace wall soot blowers are located in the walls of the furnace atthree elevations. The highest elevation is indicated as Row A with asecond elevation just above the burners designated as Row B. A third rowof blowers designated as Row C is located below the burners. Each of thefurnace walls has a general arrangement similar to that of the side wallwhich is shown in FIGURE 1. The tubes of the furnace side wall areparallel and rise vertically from the lower side wall header 7 to theupper side wall header 8. Each row of soot blowers includes four blowerson the side wall, and the side wall circuit is therefore divided intofour groups of tubes. The outlet header 8 is partitioned into foursections with each one of these sections receiving tubes from aparticular group. A single relief tube 18 carries the fluid from eachheader section to the cross-over line 9 where the fluid from all thegroups of tubes are joined and mixed. A thermocouple is located in eachof the relief tubes 18 so that the temperature of the fluid leaving eachgroup of tubes is sensed by the temperature transmitters 19.

During operation of the unit erratic slag patterns form on the furnaceWalls causing an unbalance in the heat absorption in the various groupsof tubes. This unbalance in heat absorption is reflected in the steamtemperature leaving each group of tubes as sensed by the transmitter 19.Those groups of tubes having the heaviest ash accumulation will have areduced heat absorption and therefore indicate a low temperature leavingthe particular section. In accordance with my invention the temperatureof the steam leaving each group of tubes is used to determine thelocation of the heavy slag accumulations and to determine which sootblower will be operated so that the dirtiest zones of the furnace willbe cleaned first. This is accomplished by using these temperatureimpulses to select particular blowers which are to operate whenactivated. These blowers are activated when the over-all dirtiness ofthe furnace indicates a general need for soot blowing within thefurnace.

A thermocouple in the reheat steam line senses the temperature of thereheated steam in response to which the reheat steam temperaturetransmitter 22 emits a control signal 23 to the burner tilt controller24. This controller varies the tilt of the burners 2 within the furnaceto maintain the reheat steam temperature at a preselected value. Asthefurnace walls become dirty, the heat absorption is reduced with anincreased temperature of the gases leaving the furnace, and the reheatedsteam temperature tends to increase. To compensate for this the burnersare then automatically tilted downward.

When the burners reach degrees or horizontal tilt, all the soot blowersin Row C are operated independent of any temperature measurements in therelief tubes 18. It has been found that the soot blowers below theburners are more effective when the tilts are in a horizontal or upwardposition than they are when the tilts are in a downward position. Wetherefore obtain a general cleaning of the lower portion of the furnace.As this is cleaned, the furnace becomes more efiicient and the burnerstilt upward to maintain the reheat temperature. Since the lower portionof the furnace is relatively ineffective at horizontal tilt, thecleaning of these walls does not make a great deal of difference in theheat absorption and the tilts rise only slightly to about plus degrees.The controller 28 is not reset to operate the blowers of Row C againuntil the tilts reach a plus degrees tilt and therefore the slightincrease to plus 5 degrees is insufficien-t to reset the controller. Asthe furnace dirties up,

the tilts continue downward below horizontal to maintain reheat steamtemperature.

At minus 15 degrees tilt the control signal through impulse line 29 tocontroller 30 operates to activate the soot blowers in Rows A and B. Acontrol signal therefore passes through impulse line 32 indicating aneed for soot blowing to the selector controller 33 An auctioneeringcontroller of this type is manufactured by Leeds and Northrup Company.Temperature signals indicating the temperature of the fluid leaving thevarious groups of tubes are also sent to selector controller 33 throughcontrol lines 34 from the temperature transmitters 19. This controllerselects the group of tubes having the lowest temperature and emitscontrol signal 35 to operate the soot blowers in Row A or Bcorresponding to the group of tubes having the lowest temperature. Thissignal passes to controller 37 which checks for an available blowerassociated with the particular group of tubes. This controller willalternately select Rows A and B in such a manner that if Row A had lastbeen blown in this particular group of tubes, Row B would be blown onthis occasion. This controller would also include a circuit whichprevents the soot blower from operating within one hour of the time ithas previously operated, thereby avoiding repetitive inefficientoperation of soot blowers in one particular group of tubes when the lowtemperature of the fluid leaving that circuit cannot be so corrected.When an available blower is found, the control signal is passed throughcontrol line 33 to controller 39 which acts to operate the particularwall blower. When this blower has completed its operation, controlsignal passes through control line 40 back to controller 30 to check theposition of the tilts. If the tilts are still below a plus 20 degreestilt, a control signal passes through control line 32 to again selectthe lowest temperature.

This continues until such a time as the tilts reach a plus 20 degreetilt at which time the wall blowers are deactivated and operationceases. Since the tilts are now obviously above plus 10 degree tilt,controller 28 is reset so that when the tilts reach horizontal Row Csoot blowers will again be operating.

In the particular embodiment of FIGURE 1, the overall furnace dirtinessis detected by sensing the position of the tilting burners which areoperating to control the reheat temperature. This general furnacedirtiness could also be obtained by measuring the gas temperatureleaving the furnace or by measuring spray quantity which could be usedto control reheat steam temperature, or a number of other generallyknown methods. Also row C could be incorporated with rows A and Boperating through the selector controller 33 to operate the soot blowersof row C in accordance with the temperature leaving the associated.group of tubes, although on a unit operating with tilting burners, thishas 'been found to be less elfective. Also circuits which meanderthroughout the furnace walls may be used so long as particular sootblowers are associated with various groups of tubes, and circuits may beemployed in the furnace walls which are intermeshe-d or cover only aportion of the furnace walls.

The unit illustrated in FIGURE 2 is similar to that of FIGURE 1.However, this unit includes a flow control system which regulates theflow through the furnace tubes to control the outlet temperature leavingeach group of tubes. Accordingly, the inlet header 47 is divided into anumber of sections corresponding to each. group of tubes. An individualsupply tube 48 supplies water to each header section with the flow beingcontrolled by control valves 49. The incoming water passes through line50 being distributed in the four sections of header 47 (as shown) and tocorresponding header sections .on the other walls (not shown). Thetemperature sensing transmitter 19 emits a signal through control line51 to operate the flow throttling valves 49 which, in turn, control thefiow passing through a particular group of tubes to maintain thetemperature at a predetermined value. The group of tubes having thehighest accumulation of ash will have the lowest heat absorption andtherefore the lowest flow.

Flow nozzles 52 are associated with each group of tubes and measure theflow passing through that particular group of tubes. The flow controlsignal passes through control line 54 to selector controller 53. Theembodiment of FIGURE 2 then operates in exactly the same manner as thatof FIGURE 1 with the control signal 54- passing to controller 53selecting the lowest value instead of the temperature signal passingthrough control line 34 to controller 33 selecting the lowesttemperature. Other means of determining the flow such as the position ofthe throttling valves 49 may be used.

Controllers performing the functions required are standard equipment andmay be obtained from Leeds and Northrup Company, Bailey Meter Company orHagan, Inc.

While I have illustrated and described a preferred embodiment of myinvention it is to be understood that such is merely illustrative andnot restrictive and that variations and modifications may be madetherein without departing from the spirit and scope of the invention. Itherefore do not wish to be limited to the precise details set forth butdesire to avail myself of such changes as fall within the purview of myinvention.

What I claim is:

1. A vapor generator furnace comprising: means for burning an ashbearing fuel within the furnace; a plurality of groups of tubes liningthe walls of said furnace in parallel flow relation; means for passingfluid through said tubes whereby the temperature of the fluid isincreased; means for sensing the total heat absorbed by the fluidpassing through each of said group of tubes; at least one soot blowerassociated with each group of tubes; and means for operating a sootblower associated with a group of tubes in response to the heatabsorption sensing means related to the corresponding group.

2. A vapor generator furnace comprising: means for burning an ashbearing fuel within said furnace; a plurality of groups of tubes liningthe walls of said furnace in parallel flow relation; a soot blowerassociated with each of said groups of tubes; means for passing fluidthrough said tubes whereby the temperature of said fluid is increased;means for sensing the temperature of the fluid leaving each group oftubes; and means for operating a soot blower associated with each groupof tubes in response to the means for sensing the temperature leavingthe corresponding group of tubes.

3. A furnace for a vapor generator comprising: means for burning an ashbearing fuel within said furnace; a plurality of groups of tubes liningat least a portion of the walls of said furnace in parallel flowrelation; at least one soot blower associated with each group of tubes;means for passing fluid to be heated through said groups of tubes; meansfor sensing the temperature of the fluid leaving each group of tubes;means for selecting the group of tubes with the lowest fluid temperatureleaving the group of tubes; and means for operating a soot blowerassociated with that group of tubes which is selected by said selectingmeans.

4. A furnace for a vapor generator comprising: means for burning an ashbearing fuel within said furnace; a plurality of groups of tubes liningthe walls of said furnace in parallel flow relation; at least one wallsoot blower associated with each group of tubes; means for passing fluidto be heated through said groups of tubes; means for determining theover-all furnace dirtiness; means responsive to the over-all furnacedirtiness for activating the furnace wall soot blowers; means forsensing the temperature of the fluid leaving each group of tubes; meansfor selecting the group with the lowest fluid temperature leaving andmeans for operating a soot blower associated with the group of tubeshaving the lowest fluid temperature leaving when the soot blowers areactivated in response b to the means for determining the over-allfurnace dirtiness.

5. An apparatus as in claim 4 having also a flue for the conveyance ofproducts of combustion from said furnace; steam reheating surfacelocated within said flue; means for determining the temperature of thereheated steam leaving said steam reheating means; tilting burners insaid furnace operative in response to said reheated steam temperaturesensing means to maintain the reheated steam temperature at apredetermined value; wherein the means for determining the over-allfurnace dirtiness comprises means for sensing the degree of tilt of saidtilting burners.

6. In a vapor generator furnace having furnace walls lined with aplurality of groups of tubes in parallel flow relation, and a sootblower associated with each group of tubes, the method of operationcomprising: passing fluid through each group of tubes; sensing the totalheat absorbed by the fluid passing through each group of tubes;selecting the group of tubes having the lowest heat absorption; andblowing a soot blower associated with the corresponding group of tubes.

7. In a furnace for a vapor generator having a plurality of groups oftubes lining the walls of said furnace in parallel flow relation, and asoot blower associated with each group of tubes, the method of operationcomprising: burning an ash bearing fuel within said furnace; passingfluid through said tubes in heat exchange relationship with the burningfuel; sensing the temperature of the fluid leaving each group of tubes;selecting the group of tubes having the lowest fluid temperatureleaving; and operating a soot blower corresponding to this group oftubes.

8. In a vapor generator furnace having a plurality of groups of tubeslining the walls of said furnace in parallel flow relation and a sootblower associated with each of said group of tubes, the method ofoperation comprising: burning an ash bearing fuel within said furnace;sensing the over-all furnace dirtiness; passing a fluid through saidgroup of tubes in heat exchange relationship with the burning fuel;measuring the temperature of the fluid leaving each group of tubes;selecting the group of tubes having the lowest fluid temperatureleaving; activating the soot blowers in response to the over-all furnacedirtiness; and operating the soot blowers so activated in accordancewith the selection of the group having the lowest fluid temperatureleaving.

9. A method as in claim 8 including: repeatedly operating soot blowersin response to the temperature leaving the groups of tubes; and stoppingoperation of the soot blowers when the over-all furnace dirtinessreaches a predetermined value.

10. A vapor generator furnace comprising: means for burning an ashbearing fuel within said furnace; a plurality of groups of tubes liningthe walls of said furnace; a soot blower associated with each of saidgroup of tubes; means for passing fluid through said tubes; means forsensing the temperature of the fluid leaving each of said group oftubes; means for regulating the flow through each of said group oftubes; means for controlling the flow regulating means in response tothe temperature leaving a corresponding group of tubes to maintain thetemperature leaving the group of tubes 'at a predetermined value; meansfor sensing the flow through each of said group of tubes; and means foroperating a soot blower associated with each group of tubes in responseto the flow sensing means of the corresponding group of tubes.

11. In a vapor generator furnace having a plurality of groups of tubeslining the walls of said furnace, and a soot blower associated with eachof said group of tubes, the method of operation comprising: burning anash bearing fuel within said furnace; sensing the over-all furnacedirtiness; passing a fluid through said groups of tubes in heat exchangerelationship with the burning fuel; measuring the temperature of thefluid leaving each group of tubes; regulating the flow of the fluidthrough flow through each of said group of tubes; selecting the3,274,979 7 8 each of said group of tubes to maintain the temperatureReferences Cited by the Examiner of the fluid leaving at a predeterminedvalue; sensing the UNITED STATES PATENTS group of tubes having thelowest flow; activating the 2,110,533 3/1938 et 122-392 soot blowers inresponse to over-all furnace dirtiness; 2811954 11/1957 122 392 andoperating the soot blowers so activated in accord- 31137178 6/1964calmer et 122 392 ance with the selection of the group having the lowestflow therethrough CHARLES J. MYHRE, Plzmary Exammer.

1. A VAPOR GENERATOR FURNACE COMPRISING: MEANS FOR BURNING AN ASHBEARING FUEL WITHIN THE FURNACE; A PLURALITY OF GROUPS OF TUBES LININGTHE WALLS OF SAID FURNACE IN PARALLEL FLOW RELATION; MEANS FOR PASSINGFLUID THROUGH SAID TUBES WHEREBY THE TEMPERATURE OF THE FLUID ISINCREASED; MEANS FOR SENSING THE TOTAL HEAT ABSORBED BY THE FLUIDPASSING THROUGH EACH OF SAID GROUP OF TUBES; AT LEAST ONE SOOT BLOWERASSOCIATED WITH EACH GROUP OF TUBES; AND MEANS FOR OPERATING A SOOTBLOWER ASSOCIATED WITH A GROUP OF TUBES IN RESPONSE TO THE HEATABSAORPTION SENSING MEANS RELATED TO THE CORRESPONDING GROUP.